It is easy to see that the sky is blue. Have you ever wondered why? A lot of other smart people have, too. And it took a long time to figure it out!
The light from the Sun looks white. But it is really made up of all the colors of the rainbow.
You learn that the light you see is just one tiny bit of all the kinds of light energy beaming around the Universe–and around you!
Like energy passing through the ocean, light energy travels in waves, too. Some light travels in short, “choppy” waves. Other light travels in long, lazy waves. Blue light waves are shorter than red light waves.
All light travels in a straight line unless something gets in the way to reflect it (like a mirror), bend it (like a prism), or scatter it (like molecules of the gases in the atmosphere).
Sunlight reaches Earth’s atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth’s atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.
Closer to the horizon, the sky fades to a lighter blue or white. The sunlight reaching us from low in the sky has passed through even more air than the sunlight reaching us from overhead. As the sunlight has passed through all this air, the air molecules have scattered and re-scattered the blue light many times in many directions. Also, the surface of Earth has reflected and scattered the light. All this scattering mixes the colors together again so we see more white and less blue.
Original source: http://spaceplace.nasa.gov/blue-sky/en/
1. What does the text explain?
A. The origin of the color blue
B. how the light bends
C. why the sky is blue
D. that the Sun light is white
E. how light is scattered
2. We learn from the text that … .
A. the Sun light is white
B. the Universe spreads the light
C. light energy is all around us
D. the mirror bends light
E. the prism reflects light
3. We also learn from the text that … .
A. Red light has the shortest waves
B. Green light has the longest waves
C. Yellow light has longest waves
D. Blue light has the shortest waves
E. Purple light travels in a straight line
4. If there is nothing in the way, light … .
A. travels in waves
B. bends and reflects
C. scatters everywhere
D. travels in straight line
E. is made up of many colors
5. What is it that can scatter light?
A. White color
B. surface of Earth
C. rainbow colors
D. crystal prism
E. air molecules
6. What does the word ‘figure out’ in the first paragraph mean?
A. turn out
B. find out
C. burn out
D. count on
E. call out
7. Why does the sky look blue?
A. Blue light is bent by the atmosphere
B. Blue light is dominant in the atmosphere
C. Blue light is scattered more than any other colors
D. Blue light is reflected by the atmosphere
E. Blue light is bounced to the sky
8. In the horizon, the sky tends to be … .
A. white
B. blue
C. grey
D. dark
E. yellow
